If you want to find the factorial of an integer less than 171, then you don't
need this module. Otherwise, you do need it:

var factorial =require('factorial');

factorial(170);

// => 7.257415615307994e+306

factorial(171);

// => Infinity

factorial(32768);

// => RangeError: Maximum call stack size exceeded

The Infinity problem is a result of JavaScript's limit on how big numbers can
be. This module solves this problem by using
big-integer.

The RangeError is a problem with how the factorial is calculated. The
recursion used goes so deep that it exceeds the limit that Node.js has. As
described in Reginald's blog post, this problem is solved by using trampolines.